My thought as well. All of it would be impossible, it's too disjointed, but perhaps the story of Beren and Luthien and the fight against Morgoth? Or perhaps Isildur's story from the Second Age? You could probably get a movie out of either but there isn't a great deal of material for a screenplay.
1) The Hobbit - an adaptation of the book as we know it
2) LOTR prequel - a film documenting the events between The Hobbit and the start of Fellowship